I was able to use a lot of baking soda, a little water, and a very sturdy bottle brush to get the inside of my thermos sparkling clean. It took a bit of work, but it got the job done.
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BenzoDec 18 '12 at 13:59

I have probably the same type of thermos that is made from food grade stainless steel, but still rusts a bit. I use it anyway.
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alanhJan 26 at 21:22

The problem isn't the rust per-se, it's any other thing mixed in with the iron that may be released as it oxidises that's the problem. Whether there's likely to be anything else I couldn't say, but I still stand by my original answer in that it's not a risk worth taking when it can be cleaned with a bit of effort.
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berry120Jan 8 '13 at 0:46

@berry120 I wouldn't risk it on any normal day. But based on what Dr. Wife told me, I guess it would be safe and I would do it in a more emergency/dire situation.
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theJollySinJan 24 '14 at 18:24

Sure - though in an emergency a lot of normal rules would go out the window! I was more aiming at for general use.
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berry120Jan 24 '14 at 19:33

People do not realize that their public water are delivered by iron pipes buried 20 to 80 years ago. I was an engineering student and if you cut those pipes you will see rust around the pipes. So people do not realized that they are drinking water through rusted interior of water pipes. No one has died from it.

I'd be wary of drinking from anything rusty personally - I'm not aware of the type of metal your thermos is made from, but several can start to produce potentially poisonous chemicals when they begin to oxidise. Sure, you could be ok but I wouldn't say it's worth the risk.

In terms of cleaning it, try something like Zud cleanser (readily available in the UK, not sure about other parts of the world.) Does a really good job at removing rust on anything I've tried it with!

It might oxidiz with liquids it's probably time to get a new one.
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user2907Jan 31 '14 at 2:09

Welcome to outdoors.sx.com! Your answer is about cleaning thermos but the question was about if it is safe to drink from a rusty one, so it doesn't really fit and is likely to be deleted. Please have a look on our tour page to get some more information about the site and the Q&A format.
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Benedikt BauerJan 31 '14 at 10:06

It's harmless. Rinse out anything loose. If you want, add a handfull of gravel, a cup of water, and shake for 10 minutes to get stuff out.

A thermos is going to be food grade metal. So the alloys will not be exotic ones with chromium or vanadium in quantity.

In passing: a 1 or 2 liter bottle with a pair of heavy socks pulled over it works nicely as a cheap thermos. I've used this for coffee on all day orienteering in winter, and even by day's end the coffee is at least warm.